I think these rules are a good starting point, but once you've done a few rides and experimented a bit, you find what works for you. As said above there's a big difference between bikes, the French low trail bikes have always favoured a front load. It also depends on that load, and the proportion of it you can adjust. For example, a 70kg rider with a 30kg load has the ability to manipulate more than a 90kg rider with a 10kg load. As a 100kg rider with not more than a 15kg load, I find it makes little difference how I distribute the luggage. My Mercury is very sensitive to any load over a couple of kg, but I quickly get used to it. It makes little difference to the Nomad, other than being felt on hills and generally being a bit slower, it rides the same loaded or unloaded. I have used front panniers, which do steady the steering at most riding speeds, but there's a point where that's reversed. It's a long time since I toured with four panniers, I might at some point use lightweight front fork bags, but I doubt I'll ever go the front rack route again. If I ever find myself wanting to transport huge loads, I'll use a trailer.
